Thermosyphon coolers for cooling systems with cooling towers

ABSTRACT

In one embodiment, a cooling system may include a thermosyphon cooler that cools a cooling fluid through dry cooling and a cooling tower that cools a cooling fluid through evaporative cooling. The thermosyphon cooler may use natural convection to circulate a refrigerant between a shell and tube evaporator and an air cooled condenser. The thermosyphon cooler may be located in the cooling system upstream of, and in series with, the cooling tower, and may be operated when the thermosyphon cooler is more economically and/or resource efficient to operate than the cooling tower. According to certain embodiments, factors, such as the ambient temperature, the cost of electricity, and the cost of water, among others, may be used to determine whether to operate the thermosyphon cooler, the cooling tower, or both.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/117,216, filed May 27, 2011, entitled “THERMOSYPHON COOLERS FORCOOLING SYSTEMS WITH COOLING TOWERS,” which claims priority from and thebenefit of U.S. Provisional Application Ser. No. 61/349,080, filed May27, 2010, entitled “THERMOSYPHON COOLERS FOR COOLING SYSTEMS WITHCOOLING TOWERS,” which are hereby incorporated by reference.

BACKGROUND

The invention relates generally to thermosyphon coolers, and moreparticularly, to thermosyphon coolers for use in cooling systems thatemploy cooling towers.

Cooling towers are often used to remove heat from heating, ventilating,and air conditioning (HVAC) systems, power plants, and industrialprocesses. In general, cooling towers may include nozzles that directwater down through the tower, while a fan, or free circulation, directsair up through the tower. The interaction between the air and water maypromote evaporation of a portion of the water, thereby cooling theremaining water. In open loop cooling towers, the cooling tower watermay be circulated directly through the cooling system, while in closedloop cooling towers, the cooling tower water may be directed over a heatexchanger coil that cools a separate flow of cooling fluid that in turncirculates through the cooling system.

During evaporation, water may be lost from the cooling tower andimpurities, such as salts or other dissolved solids, may be concentratedwithin the cooling tower. A portion of the cooling tower watercontaining concentrated impurities may be removed as blowdown. Toaccount for water losses due to evaporation and blowdown, makeup watermay be added to the cooling towers. Accordingly, cooling towers mayconsume very substantial quantities of water, in some cases millions ofgallons of water each year, and may be one of the largest consumers ofwater within a process.

DRAWINGS

FIG. 1 is a schematic diagram of an embodiment of a cooling system thatemploys a thermosyphon cooler and an open loop cooling tower.

FIG. 2 is a perspective view of an embodiment of the thermosyphon coolershown in FIG. 1.

FIG. 3 is a schematic diagram of an embodiment of the thermosyphoncooler shown in FIG. 1.

FIG. 4 is a schematic diagram of another embodiment of a cooling systemthat employs a thermosyphon cooler and an open loop cooling tower.

FIG. 5 is a schematic diagram of an embodiment of a cooling system thatemploys a thermosyphon cooler and a closed loop cooling tower.

FIG. 6 is a flow chart depicting a method for operating a thermosyphoncooler.

FIG. 7 is a flow chart continuing the method for operating athermosyphon cooler shown in FIG. 6.

FIG. 8 is a chart depicting inputs and outputs that may be employed tooperate a thermosyphon cooler.

FIG. 9 is a schematic diagram of an embodiment of a cooling system thatemploys a dry heat rejection system and an open loop cooling tower.

FIG. 10 is a flow chart depicting a method for operating a dry heatrejection system.

FIG. 11 is a schematic diagram of another embodiment of a cooling systemthat employs a thermosyphon cooler and an open loop cooling tower.

FIG. 12 is a flow chart depicting another embodiment of a method foroperating a thermosyphon cooler.

FIG. 13 is a schematic diagram of another embodiment of a cooling systemthat employs a thermosyphon cooler and a cooling tower.

FIG. 14 is a schematic diagram of a prior art cooling system thatincludes a cooling tower.

FIG. 15 is a schematic diagram depicting retrofitting of the prior artcooling system of FIG. 14 to include an embodiment of a thermosyphoncooler system.

FIG. 16 is a schematic diagram depicting retrofitting of the prior artcooling system of FIG. 14 to include another embodiment of athermosyphon cooler system.

DETAILED DESCRIPTION

The present disclosure is directed to thermosyphon coolers that may beemployed in cooling systems that use cooling towers. As used herein, theterm “cooling tower” includes open loop and closed loop cooling towersthat cool a fluid, such as water, by evaporative cooling using ambientair. Cooling towers may be particularly useful for cooling processfluids due to the relatively low temperatures that may be achieved byevaporative cooling, as compared to dry cooling. Further, cooling towersmay provide flexibility in determining a system layout because thecooling towers may be located farther away from a process, allowing realestate in the vicinity of the cooled building or process to be used forother purposes. However, due to the evaporative cooling, cooling towersmay consume large amounts of water. To conserve water, it may bedesirable to employ other types of cooling systems in conjunction withcooling towers, particularly in areas where water is in short supplyand/or is costly.

Accordingly, the present disclosure is directed to dry heat rejectionsystems, such as thermosyphon coolers, that may be employed to provideadditional and/or alternative cooling in cooling systems that includecooling towers. The thermosyphon coolers may be located in coolingsystems upstream of, and in series with, the cooling towers, and may beoperated when the thermosyphon coolers are more economically and/orresource efficient to operate than the cooling towers. For example, whenambient temperatures are low, it may be beneficial to operate thethermosyphon coolers to reduce water consumption of the cooling towers.When ambient temperatures are high, it may be desirable to operate thecooling towers to provide the lower process cooling fluid temperaturesthat may be achieved through evaporative cooling. According to certainembodiments, factors, such as the ambient temperature, the cost ofelectricity, the cost of water, the temperature of the heated coolingfluid exiting the process heat exchanger, and the desired temperature ofthe cooling fluid entering the process heat exchanger, among others, maybe used to determine whether to operate the thermosyphon coolers, thecooling towers, or both.

In an exemplary arrangement, a thermosyphon cooler will include a shelland tube evaporator and an air cooled condenser. The cooling tower watermay flow through the tubes of the evaporator and may transfer heat torefrigerant circulating between the evaporator and the air cooledcondenser. The thermosyphon cooler may be designed to minimize thepressure drop within the system so that the refrigerant is circulatedbetween the evaporator and the condenser through natural convection. Asused herein, the term “natural convection” means circulation of a fluidwithout mechanical force, for example, without mechanical force asprovided by a pump or a compressor. According to certain embodiments,the buoyancy of the heated refrigerant and the height difference betweenthe air cooled condenser and the evaporator may provide the drivingforce for circulating the refrigerant through natural convection.Because the refrigerant may be circulated using natural convection, thecondenser fans and their motor(s) may be the only moving parts in thethermosyphon cooler. Accordingly, the thermosyphon coolers may haverelatively low rates of energy consumption and maintenance when comparedto traditional dry coolers that implement pumped freeze protectantcooling loops.

The evaporator within the thermosyphon cooler also may include accesscovers and/or removable components that allow the interior of theevaporator tubes to be cleaned. Accordingly, the thermosyphon coolersmay be particularly well-suited for circulating cooling tower water inopen loop cooling tower systems where the water may be exposed todissolved solids and other contaminants. Further, the thermosyphoncooler may include a freeze protection system, which may allow thethermosyphon cooler to cool the cooling tower water directly, ratherthan employing a separate loop, which contains a freeze protectant, suchas glycol.

FIG. 1 is a schematic view of a cooling system 10 that employs athermosyphon cooler 12 and a cooling tower 14. The cooling system 10 maybe primarily located within a building 16 or area that is maintained attemperatures above freezing. However, certain components of coolingsystem 10, such as thermosyphon cooler 12 and cooling tower 14, may belocated outside of building 16, for example, on the roof of building 16.Further, in other embodiments, cooling tower 14 may be located adistance away from building 16 or the process area and, in certainembodiments, may be located at ground level.

Cooling system 10 includes a process heat exchanger 18 that may be usedto transfer heat from a process loop 20 to a cooling system loop 22.According to certain embodiments, process loop 20 may circulate aprocess fluid, such as refrigerant, steam, or other vapor to becondensed. For example, process loop 20 may circulate compressedrefrigerant vapor to be condensed from a water chiller. In anotherexample, process loop 20 may circulate steam to be condensed from asteam turbine. In another example, process loop 20 may circulate aprocess fluid for an industrial process that may require cooling.

Cooling system loop 22 may circulate a fluid to be cooled, such as wateror a mixture of water and other components. As the cooling fluid flowsthrough process heat exchanger 18, the cooling fluid may absorb heatfrom the process fluid. According to certain embodiments, anintermediate fluid, such as refrigerant may be used to transfer heatfrom the process fluid within process loop 20 to the cooling fluidwithin cooling system loop 22. For example, in certain embodiments,process heat exchanger 18 may be a water cooled condenser that is partof a chiller that circulates a refrigerant to transfer heat from processloop 20 to cooling system loop 22. In these embodiments, the processfluid may flow through an evaporator of the chiller. However, in otherembodiment, the intermediate fluid may be omitted and the process heatexchanger 18 may be used to transfer heat directly from the processfluid to the cooling fluid. Moreover, in yet other embodiments, processheat exchanger 18 may be omitted and the cooling fluid within coolingsystem loop 22 may be circulated directly to the process to be cooled.

As the cooling fluid flows through process heat exchanger 18, thecooling fluid may absorb heat from the process fluid. Accordingly heatedcooling fluid may exit process heat exchanger 18 and may flow throughcooling system loop 22 through a valve 24 to thermosyphon cooler 12. Incertain embodiments, a pump may be included to circulate the coolingfluid to thermosyphon cooler 12 from valve 24. However, in otherembodiments, the pump may be omitted.

The heated cooling fluid may enter thermosyphon cooler 12 where thecooling fluid may be cooled. As described below with respect to FIGS. 2and 3, thermosyphon cooler 12 may include a shell and tube evaporator 76and an air cooled condenser 78. A refrigerant loop 80 may be employed totransfer heat from the cooling fluid flowing through shell and tubeevaporator 76 to air cooled condenser 78. Heat may be rejected fromthermosyphon cooler 12 through ambient air directed over air cooledcondenser 78 by one or more fans 26 driven by one or more motors 28.According to certain embodiments, motors 28 may incorporate variablespeed drives (VSD's) that allow the speed of fans 26 to be adjusted toincrease and decrease the amount of cooling provided by thermosyphoncooler 12. Further, in certain embodiments, motors 28 may beelectronically commutated motors (ECM's), which allow the fan speed tobe adjusted. The cooling fluid may then exit thermosyphon cooler 12 andmay flow through valves 30 and 32 to cooling tower 14, where the coolingfluid may be further cooled through evaporative cooling.

Within cooling tower 14, the cooling fluid may be cooled via evaporativecooling with ambient air. The cooling fluid may enter cooling tower 14through nozzles 34 that direct the cooling fluid down through coolingtower 14 over a fill material 36, such as splash bars, sheet fill packs,or any other suitable surface. A fan 38 driven by a motor 40 may directair up through cooling tower 14 so that the air mixes with the coolingfluid flowing through cooling tower 14 to promote evaporative cooling.According to certain embodiments, fan 38 may be a centrifugal or axialfan driven by a VSD or ECM. However, in other embodiments, fan 38 may beomitted and air movement within the cooling tower would be induced bynatural convection. Cooling tower 14 may be a crossflow or a counterflowcooling tower. Further, although shown as an induced draft coolingtower, in other embodiments, cooling tower 14 may be a forced draftcooling tower.

The cooled cooling fluid may then exit cooling tower 14 and may becollected within a sump 42. As shown, sump 42 is located within building16, which, in certain embodiments, may inhibit freezing of the coolingfluid within sump 42. However, in other embodiments, sump 42 may be anintegral part of cooling tower 14 and may be located outside of building16, as described further below with respect to FIG. 4.

As the cooling fluid flows through cooling tower 14 and contacts ambientair, solids and other contaminants may become entrapped or entrainedwithin the cooling fluid. Additional minerals, salts, and othercontaminants may enter the cooling fluid with make-up water. As purewater is removed from the cooling fluid through evaporation, theconcentration of such contaminants will increase within the coolingfluid. Accordingly, a portion of the cooling fluid, which may containparticulates, dissolved solids, and/or contaminants, may be removed asblowdown by opening a valve 46. A valve 44 also may be opened to directmakeup cooling fluid into sump 42 to account for losses in the coolingfluid due to blowdown and evaporation. A flow meter 47 may be employedto measure the amount of water that is supplied to sump 42 through valve44 as makeup water. For example, flow meter 47 may measure the flow rateof water supplied to sump 42, and the flow rate data may be provided toa controller 50, which in turn may calculate the amount of makeup waterthat is supplied to sump 42. In certain embodiments, controller 50 mayuse the flow rate data from flow meter 47 to calculate the water costsof operating cooling system 10. The cooled cooling fluid from sump 42may then be returned to process heat exchanger 18 via a pump 48 wherethe cooling fluid may again absorb heat from the process fluidcirculating within process fluid loop 20.

Cooling system 10 also may include a controller 50 that governsoperation of cooling system 10. Controller 50 may receive input signals52 from components, such as valves and sensors within system 10, in theform of analog and/or digital inputs as shown in FIG. 8. Based on theinput signals, controller 50 may send output signals 54, such as analogand/or digital outputs shown in FIG. 8, to vary operation of coolingsystem 10. As described further below with respect to FIGS. 6 and 7,controller 50 may use the input and output signals 52 and 54 to enableoperation of thermosyphon cooler 12 whenever it is efficient to operatethermosyphon cooler 12 in addition to, or instead of cooling tower 14.

According to certain embodiments, controller 50 also may governoperation of a freeze protection system 56 included within coolingsystem 10. Freeze protection system 56 may include a differentialpressure switch 58 that measures the pressure difference between thecooling fluid entering and exiting thermosyphon cooler 12 and atemperature sensor 57 that measures the temperature of the refrigerantwithin the shell side of evaporator 76. Controller 50 may use inputsignals 52 from differential pressure switch 58 to determine whethercooling fluid is flowing through thermosyphon cooler 12. If controller50 detects that there is no cooling fluid flow based on input fromdifferential pressure switch 58, controller 50 may initiate a lowtemperature protection mode of freeze protection system 56, which mayinhibit freezing of the cooling fluid used within thermosyphon cooler12. To initiate the low temperature protection mode, controller 50 mayclose a valve 93 to promote collection of the refrigerant withincondenser 78. The lack of refrigerant flow to evaporator 76 may inhibitfreezing of the cooling fluid within evaporator 76. Controller 50 alsomay turn on supplemental heat for evaporator 76 to provide an influx ofheat to evaporator 76 to inhibit freezing of the cooling fluid includedwithin evaporator 76.

Controller 50 also may use input from temperature sensor 57 to governoperation of freeze protection system 56. For example, when controller50 receives an input from temperature sensor 57 that indicates that thetemperature within evaporator 76 is below a certain set point,controller 50 may initiate a freeze protection mode of freeze protectionsystem 56, which may drain the cooling fluid from thermosyphon cooler 12and may divert the flow of the cooling fluid around thermosyphon cooler12. To drain the cooling fluid from thermosyphon cooler 12, controller50 may open valves 60 and 62 to direct the cooling fluid to a drain line64. As shown, drain line 64 may direct the cooling fluid to sump 42.However, in other embodiments, for example, where sump 42 is locatedoutside of building 16, drain line 64 may be connected to a sewer or acollection reservoir.

Controller 50 also may close valve 30 to direct cooling fluid exitingthermosyphon cooler 12 to drain line 64 through valve 62. Further,controller 50 may open a valve 66 to inject air into thermosyphon cooler12 to facilitate drainage of the cooling fluid from thermosyphon cooler12. According to certain embodiments, valve 66 may be designed to injectair into the evaporator tubes of thermosyphon cooler 12 to displace thecooling fluid from the evaporator tubes. To inhibit the flow ofadditional cooling fluid into thermosyphon cooler 12, controller 50 alsomay change the position of valve 24 to direct the cooling fluid fromprocess heat exchanger 18 to bypass thermosyphon cooler 12 and flowdirectly to valve 32. According to certain embodiments, valves 60, 62,and 66 may be solenoid valves designed to fail in the open position,which, in the event of a power failure, may automatically enable freezeprotection system 56.

Cooling system 10 also may include temperature sensors 68, 70, 72, and74 that may be used to detect temperatures used by controller 50 togovern operation of cooling system 10. For example, temperature sensor68 may detect the ambient air temperature; temperature sensor 70 maydetect the temperature of the cooling fluid exiting thermosyphon cooler12; temperature sensor 72 may detect the temperature of the coolingfluid exiting process heat exchanger 18; and temperature sensor 74 maydetect the temperature of the cooling fluid entering process heatexchanger 18. Temperature sensors 68, 70, 72, and 74 may provide thetemperatures to controller 50 in the form of input signals 52, which maybe used to control operation of cooling system 10.

According to certain embodiments, controller 50 may use temperaturessensed by some, or all of the sensors 57, 68, 70, 72, and 74 todetermine when to enable freeze protection system 56. For example,controller 50 may initiate the low temperature protection mode of freezeprotection system 56 when there is no flow, as detected by differentialpressure switch 58, and when the ambient temperature, as detected bysensor 68, is below an ambient temperature set point. In anotherexample, controller 50 may disable a freeze protection mode of freezeprotection system 56 when the temperature of the cooling fluid exitingthermosyphon cooler 12, as detected by sensor 70, is above anintermediate temperature set point.

Controller 50 also may use temperatures sensed by some, or all of, thesensors 57, 68, 70, 72, and 74 to determine operating parameters ofthermosyphon cooler 12. According to certain embodiments, cooling system10 may be designed to cool the cooling fluid entering process heatexchanger 18 to a specific temperature, which may be referred to as thecooling system temperature set point. If the temperature of the coolingfluid entering process heat exchanger 18, as detected by sensor 74, isabove the cooling system temperature set point, controller 50 mayprovide output signals to motor 28 to increase the speed of thecondenser fans 26. Similarly, if the temperature of the cooling fluidentering process heat exchanger 18, as detected by sensor 74, is belowthe cooling system temperature set point, controller 50 may provideoutput signals to motor 28 to decrease the speed of the condenser fans26.

Controller 50 also may use temperatures sensed by some, or all of thesensors 57, 68, 70, 72, and 74 to determine when to operate coolingtower 14. For example, if the temperature of the cooling fluid exitingthermosyphon 12, as detected by sensor 70, is equal to or below thecooling system temperature set point, controller 50 may provide anoutput signal to valve 32 to change the position of valve 32 so that thecooling fluid bypasses cooling tower 14 and proceeds directly to sump42. In this mode of operation, thermosyphon cooler 12 may be capable ofproviding enough cooling capacity to achieve the cooling systemtemperature set point, and accordingly, cooling system 10 may beoperated without employing cooling tower 14, which may reduce waterconsumption within cooling system 10.

As described further below with respect to FIGS. 6 and 7, controller 50also may use temperatures sensed by some, or all of the sensors 57, 68,70, 72, and 74 to determine when to operate thermosyphon cooler 12. Forexample, controller 50 may use temperatures sensed by sensors 72 and 68to determine the temperature difference between the cooling fluidexiting process heat exchanger 18 and the ambient air. Controller 50 maythen use this temperature difference in conjunction with water andelectricity rates to determine when it is economically and/or resourceefficient to operate thermosyphon cooler 12. As described further belowwith respect to FIGS. 6 and 7, controller 50 may selectively enableoperation of the thermosyphon cooler based on the temperaturedifference, water costs, and/or electricity costs. In these embodiments,controller 50 may send output signals to equipment, such as valves 24,30, and 32, among, others to selectively enable or disable thethermosyphon cooler. In other embodiments, controller 50 may determinewhether the thermosyphon cooler should be enabled or disabled and mayoutput this recommendation to a display. An operator may then view therecommendation and adjust operation of the cooling system based on therecommendation.

FIGS. 2 and 3 depict an embodiment of thermosyphon cooler 12. As shownin FIG. 2, thermosyphon cooler 12 includes a shell and tube evaporator76 and an air cooled condenser 78. Shell and tube evaporator 76 mayreceive heated cooling fluid from process heat exchanger 18 (FIG. 1) andmay transfer heat from the cooling fluid to refrigerant flowing throughthe evaporator 76. According to certain embodiments, the refrigerant maybe an HFC or an HFO type refrigerant; however, in other embodiments, anysuitable refrigerant may be employed. The heated refrigerant may bedirected through piping of refrigerant loop 80 to condenser 78, wherethe refrigerant may be cooled by ambient air directed through condenser78 by fans 26. The cooled refrigerant may then be returned to evaporator76 through refrigerant loop 80. According to certain embodiments,evaporator 76 and condenser 78 may be included within a common frame 82that allows thermosyphon cooler 12 to be sold as a single integratedpackage. However, in other embodiments, evaporator 76 and condenser 78may be disposed within separate frames or may be installed withinseparate parts of cooling system 10. Further, although the embodimentreflected in FIG. 2 and FIG. 3 shows evaporator 76 as a shell and tubeevaporator, other embodiments may include another type of evaporator,such as a plate evaporator design, in lieu of a shell and tube design.

The refrigerant and the cooling fluid may circulate through thermosyphoncooler 12 as shown in FIG. 3. Shell and tube evaporator 76 may include ashell 84 that contains the refrigerant as the refrigerant flows throughevaporator 76. Shell 84 also may house tubes 85 that circulate thecooling fluid through evaporator 76. The cooling fluid may enter tubes85 through an inlet 86 and may exit tubes 85 through an outlet 87. Asthe cooling fluid flows through tubes 85, the cooling fluid may transferheat to the refrigerant flowing within shell 84. As the refrigerantabsorbs heat, the heated refrigerant, which is more buoyant than thecooler refrigerant, may be drawn by natural convection through piping ofrefrigerant loop 80 into condenser 78, which is at a lower temperaturethan evaporator 76. The heated refrigerant may then flow through a heattransfer coil 88 included within condenser 78 and fans 26 may drawenvironmental air over coil 88 to cool the refrigerant flowing withincoil 88. The cooled refrigerant may then return by gravity to shell 84where the refrigerant may again absorb heat from the cooling fluidwithin tubes 85.

To promote the return of the cooled refrigerant into evaporator 76,condenser 78 may be disposed at a height 89 above evaporator 76 topromote the return of cooled refrigerant to evaporator 76. Condenser 78,evaporator 76, and piping of refrigerant loop 80 may be sized tominimize the pressure drop within thermosyphon cooler 12, therebyallowing a lower height 89 to be employed to return refrigerant fromcondenser 78 to evaporator 76 through natural convection. According tocertain embodiments, height 89 may be less than approximately 10 to 12feet to allow thermosyphon cooler 12 to be shipped as a singleintegrated package on a conventional road truck. However, in otherembodiments, height 89 may be any suitable height. In certainembodiments, evaporator 76 also may be disposed at an angle to promotedrainage of cooling fluid from evaporator 76. According to certainembodiments, evaporator 76 may be tilted at an angle of approximately 5degrees with respect to horizontal.

Evaporator 76 may be designed as a cleanable evaporator where theinterior of tubes 85 may be accessed for cleaning to remove contaminantbuildup from particulates and/or dissolved solids that enter tubes 85with the cooling fluid. For example, the cooling fluid may absorb solidsfrom the environmental air that contacts the cooling fluid in coolingtower 14. To provide access to tubes 85, evaporator 76 may include anaccess cover 90 that may be removed to expose openings into tubes 85.Further, in other embodiments, instead of, or in addition to a removableaccess cover 90, evaporator 76 may include a removable head section 91that may allow access to tubes 85 for cleaning.

In certain embodiments, evaporator 76 also may include a sensor 92, suchas an optical sensor, designed to detect the level of the cooling fluidwithin evaporator 76. In these embodiments, sensor 92 may be used inconjunction with freeze protection system 56 to ensure that the coolingfluid has been drained from evaporator 76 when the freeze protectionmode of freeze protection system 56 has been enabled. Further, incertain embodiments, thermosyphon cooler 12 may include a valve 93disposed within piping of refrigerant loop 80 to stop the flow ofrefrigerant through refrigerant loop 80. In these embodiments, valve 93may be closed by controller 50 upon detecting a condition, such as a lowambient temperature, low evaporator temperature, for example, measuredat temperature sensor 92, and/or no flow within thermosyphon cooler 12,that may produce freezing. When closed, valve 93 may promote collectionof the refrigerant within coil 88 of condenser 78, which may inhibitcirculation of the refrigerant within refrigerant loop 80 and prohibitcirculation of refrigerant to evaporator 76. Evaporator 76 also mayincorporate supplemental heating and/or insulation, to provide an influxof heat to evaporator 76 upon detecting a potential freeze condition.For example, in certain embodiments, evaporator 76 may include heattracing and/or cartridge heaters that can be turned on to provide heatwhen a potential freeze condition is detected.

FIG. 4 depicts another embodiment of the cooling system 10 that includesopen loop cooling tower 14 and thermosyphon cooler 12. The embodiment ofcooling system 10 shown in FIG. 4 is generally similar to the embodimentof cooling system 10 described above with respect to FIG. 1. However,the cooling tower 14 shown in FIG. 4 includes an integrated sump 42rather than a sump that is disposed within building 16, as shown in FIG.1.

As shown in FIG. 4, the cooling fluid may be cooled within thermosyphoncooler 12. Thermosyphon cooler 12 includes freeze protection system 56,which may operate as described above with respect to FIG. 1. However,drain line 64 may be directed to a sewer or collection reservoir, ratherthan to sump 42. The cooling fluid exiting thermosyphon cooler 12 mayflow through valve 32 to cooling tower 14. Within cooling tower 14, thecooling fluid may be directed over fill material 36 by nozzles 34 andmay collect within sump 42, which may be located in the lower portion ofcooling tower 14. Valve 44 may be opened to direct makeup cooling fluidinto sump 42 to account for losses in the cooling fluid due to blowdownand evaporation. Flow meter 47 may be employed to measure the amount ofwater that is provided to sump 42. Valve 46 also may be opened to removeblowdown from cooling tower 14. The cooled cooling fluid from sump 42may then be returned to process heat exchanger 18 via pump 48. Withinprocess heat exchanger 18, the cooling fluid may again absorb heat fromthe process fluid circulating within process fluid loop 20.

As described above with respect to FIGS. 1 through 4, thermosyphoncooler 12 may be employed in a cooling system 10 that includes an openloop cooling tower where environmental air may directly contact thecooling fluid flowing through cooling system 10. However, in otherembodiments, thermosyphon cooler 12 may be employed within a closedcircuit cooling tower as shown in FIG. 5. Closed loop cooling towers maybe particularly useful in systems where it may be desirable to reducecontaminants in the cooling fluid.

The embodiment of the cooling system 10 shown in FIG. 5 may be generallysimilar to the cooling system described above with respect to FIG. 1.However, rather than allowing the cooling fluid within cooling systemloop 22 to be directly exposed to the ambient air within cooling tower14 as in FIG. 1, cooling system 10 in FIG. 5 is isolated from contactingambient air by employing closed circuit cooling tower 94 in lieu ofcooling tower 14. Within closed circuit cooling tower 94, the coolingfluid flowing through cooling system loop 22 may be cooled by closedcircuit cooling tower cooling coil 95 which may transfer heat to a spraywater loop 96 that is integral to closed circuit cooling tower 94. Thespray water circulating within spray water loop 96 may be cooled viaevaporative cooling with ambient air, thus enabling the cooling fluidflowing through cooling system loop 22 from being exposed to theairborne and makeup water borne contaminants normally associated withopen cooling system loops. The spray water loop may include nozzles 34which direct the spray water over the closed circuit cooling towercooling coil 95, a sump 42 to collect the spray water, spray waterpiping 97, and a spray water pump 98. A fan 38 driven by a motor 40 maydirect air up through closed circuit cooling tower 94 to promoteevaporative cooling of the spray water. A blowdown valve 46 may be usedto remove contaminants from spray water loop 96 and makeup water valve44 may be used to direct makeup spray water into sump 42 to account forlosses in spray water due to blowdown and evaporation. Further, flowmeter 47 may be employed to measure the amount of water that is providedto sump 42.

FIG. 6 depicts a method 100 that may be employed to govern operation ofa cooling system 10 that includes an open loop cooling tower, as shownin FIGS. 1 and 4, or a closed loop cooling tower, as shown in FIG. 5.According to certain embodiments, controller 50 may include a processorthat executes code to perform method 100. The executable code mayinclude instructions for performing method 100 and may be stored in anon-transitory, tangible, computer readable medium, such as a volatileor non-volatile memory, which in certain embodiments may be included incontroller 50.

Method 100 may begin by determining (block 102) whether cooling system10 is beginning operation. For example, cooling system 10 may beginoperation upon startup of process heat exchanger 18. If cooling system10 is beginning operation, controller 50 may initiate (block 103) afreeze protection mode of freeze protection system 56. To initiate thefreeze protection mode, controller 50 may position valve 24 to directthe cooling fluid to bypass thermosyphon cooler 12. Controller 50 alsomay leave valves 60, 62, and 66 in the open position. Further,controller 50 may close valve 93 to stop the flow of refrigerant withinrefrigerant loop 80 of thermosyphon cooler 12.

If cooling system 10 is not beginning operation, controller 50 maydetermine (block 104) whether to initiate a low temperature protectionmode of freeze protection system 56. For example, controller 50 mayreceive the ambient temperature as an input from temperature sensor 68and may determine whether the ambient temperature is below an ambienttemperature set point, which, in certain embodiments, may be 36° F.However, in other embodiments, the ambient temperature set point mayvary. If the ambient temperature is below the ambient temperature setpoint, controller 50 may then determine if there is flow throughthermosyphon cooler 12. For example, controller 50 may detect flowthrough thermosyphon cooler 12 using differential pressure switch 58.

If controller 50 determines that there is no flow through thermosyphoncooler 12, controller 50 may initiate (block 105) the low temperatureprotection mode of freeze protection system 56. The low temperatureprotection mode may allow the cooling fluid to be retained withinthermosyphon cooler 12 during relatively short periods of low ambienttemperatures and/or during relatively short periods of shutdown ofcooling system 10. For example, low temperature protection mode may beinitiated when cooling system 10 is shutdown overnight when there is nocooling demand from process heat exchanger 18.

To initiate the low temperature protection mode, controller 50 mayadjust operation of cooling system 10 to protect the cooling fluidwithin thermosyphon cooler 12 from freezing. For example, controller 50may turn off the thermosyphon cooler fans 26. Controller 50 also mayensure that valves 24 and 30 are open to allow the cooling fluid to flowthrough thermosyphon cooler 12. Further, controller 50 may close valve93 to stop the flow of refrigerant through refrigerant loop 80. Closingvalve 93 may allow the refrigerant to collect within condenser 78, whichmay inhibit freezing of the cooling fluid within evaporator 76.Controller 50 also may turn on the supplemental heat for evaporator 76,which may provide heat to evaporator 76 to inhibit freezing of thecooling fluid contained within evaporator 76.

If there is flow through thermosyphon cooler 12 and/or if the ambienttemperature is above the ambient temperature set point, controller 50may then determine (block 106) whether the evaporator temperature isbelow an evaporator temperature set point. For example, controller 50may receive the evaporator temperature as an input from temperaturesensor 57, which may indicate the temperature of the refrigerant withinthe shell side of evaporator 76. According to certain embodiment, theevaporator temperature set point may be 33° F. However, in otherembodiments, the evaporator temperature set point may vary.

If controller 50 determines that the evaporator temperature is below theevaporator temperature set point, controller 50 may initiate (block 108)the freeze protection mode of freeze protection system 56. To initiatethe freeze protection mode, controller 50 may adjust operation ofcooling system 10 so that the cooling fluid bypasses thermosyphon cooler12. In particular, controller 50 may turn off the thermosyphon coolerfans 26 and may divert water away from thermosyphon cooler 12 usingvalve 24. Controller 50 also may position valve 32 to direct the coolingfluid exiting thermosyphon cooler 12 directly to sump 42. After thecooling fluid has drained from thermosyphon cooler 12, controller 50 mayposition valve 32 to allow the cooling fluid to flow through coolingtower 14, where the cooling fluid may be cooled by evaporative cooling.

In the freeze protection mode, controller 50 also may drain coolingfluid from thermosyphon cooler 12. For example, controller 50 may closevalve 30 and open valves 60 and 62 to direct the cooling fluid withinthermosyphon cooler 12 to drain line 64. Controller 50 also may openvalve 66 to inject air into thermosyphon cooler 12 to further promotedrainage of the cooling fluid from thermosyphon cooler 12. According tocertain embodiments, draining the cooling fluid from thermosyphon cooler12 in freeze protection mode may protect tubes 85 from damage due toexpansion and/or freezing of the cooling fluid.

If controller 50 determines that the freeze protection mode should notbe initiated, controller 50 may then determine (block 110) whether thefreeze protection mode should be disabled. First, controller 50 maydetermine whether freeze protection mode is currently enabled, forexample, based on the positions of valves 24, 60, 62, 66, and 30. Iffreeze protection mode is currently enabled, controller 50 may thendetermine whether the intermediate temperature (i.e. the temperature ofthe cooling fluid exiting thermosyphon cooler 12), as measured bytemperature sensor 70, is above an intermediate temperature set point,which, in certain embodiments, may be approximately 50° F. However, inother embodiments, the intermediate temperature set point may vary.

If the intermediate temperature is not above the intermediatetemperature set point, controller 50 may allow cooling system 10 tocontinue operating in the freeze protection mode. However, if theintermediate temperature is above the intermediate temperature setpoint, controller 50 may initiate (block 112) a freeze restart sequenceto allow the cooling fluid to flow through thermosyphon cooler 12. Inparticular, controller 50 may close drain valves 60 and 62 and also mayclose vent valve 66. Further, controller 50 may adjust the positions ofvalves 24 and 30 to allow the cooling fluid to flow through thermosyphoncooler 12. Accordingly, cooling system 10 may now be operating in aprocess cooling mode where the cooling fluid flows through thermosyphoncooler 12 to be cooled by the ambient air.

As shown in FIG. 7, method 100 may then continue by determining (block114) whether cooling system 10 is operating in a process cooling mode.In the process cooling mode, cooling system 10 may be set so that thecooling fluid is directed through both thermosyphon cooler 12 andcooling tower 14. According to certain embodiments, controller 50 maydetect operation in the process cooling mode based on inputs from motors28 and 40 and valves 24 and 32. If controller 50 detects that coolingsystem 10 is not operating in the process cooling mode, controller 50may leave cooling system 10 operating in its current mode. For example,if cooling system 10 is not operating in the process cooling mode,cooling system 10 may be operating in the freeze protection mode or inthe low temperature mode.

If cooling system 10 is operating in the process cooling mode,controller 50 may then perform (block 116) calculations that may be usedto determine (block 118) whether cooling with thermosyphon cooler 12should be enabled. For example, controller 50 may calculate thethermosyphon economic power consumption limit (TEPCL). As shown in FIG.8, the TEPCL may be the maximum kilowatts of electricity that should beused by condenser fans 26 per degree of cooling fluid temperature dropachieved by thermosyphon cooler 12 to ensure that the avoided watercosts are greater than the incremental electricity costs used to operatethermosyphon cooler 12.

The TEPCL may be calculated using inputs such as the cost of water, thecost of electricity, ambient wet bulb and dry bulb temperatures, coolingtower water usage (e.g., measured by flow meter 47), the cost of wastewater, the cost of water treatment, and/or cooling tower fan powerconsumption, among others. The costs of water and electricity may beinput by an operator or may be obtained by controller 50 over a networkconnection. Using the water and electricity rates, controller 50 maycalculate the TEPCL as the maximum kilowatts that should be used by thecondenser fan motors 28 per degree of cooling as measured by thetemperature difference between the temperature of the cooling fluidexiting process heat exchange 18, as measured by sensor 72, and thetemperature of the cooling fluid exiting thermosyphon cooler 12 (i.e.the intermediate temperature), as measured by sensor 70.

The TEPCL may be used to calculate a thermosyphon start threshold (TST).As shown in FIG. 7, the thermosyphon start threshold may be the minimumtemperature difference that should exist between the temperature of thecooling fluid exiting process heat exchanger 18, as measured bytemperature sensor 72, and the ambient air temperature, as measured bytemperature sensor 68, to allow the thermosyphon cooler 12 to beoperated at an economic power consumption level below the TEPCL whencondenser fans 26 are operated at a low fan speed.

Controller 50 may then use the calculated TST to determine (block 118)whether the actual temperature difference between the cooling fluidexiting process heat exchanger 18 and the ambient air temperature isgreater than the TST. For example, controller 50 may calculate theactual temperature difference based on the temperatures received fromsensors 72 and 68. If the actual temperature difference is below theTST, controller 50 may disable (block 120) operation of thermosyphoncooler 12. For example, controller 50 may position valve 24 so that thecooling fluid bypasses thermosyphon cooler 12. Further, in certainembodiments, controller 50 may turn off condenser fans 26.

Moreover, in certain embodiments, controller 50 also may determinewhether an ambient temperature is above a high temperature set point.For example, controller 50 may receive an input from temperature sensor68 that indicates the ambient temperature. If the ambient temperature isabove the high temperature set point, controller 50 may disable (block120) operation of thermosyphon cooler 12. According to certainembodiments, the high temperature set point may be the ambienttemperature above which heat would be added to the cooling fluid flowingthrough thermosyphon cooler 12. Accordingly, in certain embodiments, thehigh temperature set point may depend on the temperature of the coolingfluid exiting process heat exchanger 18, which may be detected bytemperature sensor 72. In situations where the ambient temperature isapproximately equal to or higher than the temperature of the coolingfluid exiting process heat exchanger 18, it may be desirable to bypassthermosyphon cooler 12 to avoid adding heat from the ambient air to thecooling fluid.

If, on the other hand, controller 50 determines (block 118) that theambient temperature is below the high temperature set point and/or ifthe actual temperature difference is greater than the TST, controller 50may enable (block 122) operation of thermosyphon cooler 12. For example,controller 50 may position valve 24 to allow the cooling fluid to flowthrough thermosyphon cooler 12. Accordingly, the cooling fluid may flowthrough thermosyphon 12 where the fluid may be cooled by the ambientair.

After thermosyphon cooler 12 is enabled, controller 50 may then adjustoperation of fans 26 to vary the amount of cooling provided bythermosyphon cooler 12. According to certain embodiments, the operationof fans 26 may be adjusted to minimize consumption of electricity whilestill providing the desired amount of cooling. For example, controller50 may determine (block 124) whether the intermediate temperature, asmeasured by temperature sensor 70, is below the cooling systemtemperature set point. When the intermediate temperature is at or belowthe cooling system temperature set point, which is the desiredtemperature of the cooling fluid entering process heat exchanger 18,thermosyphon cooler 12 may be capable of providing enough cooling toachieve the cooling system temperature set point, without additionalcooling from cooling tower 14. Further when the intermediate temperatureis below the cooling system temperature set point, thermosyphon 12 maybe currently overcooling the cooling fluid, and accordingly, the speedof condenser fans 26 may be reduced.

If the intermediate temperature is below the cooling system temperatureset point, controller 50 may then determine (block 126) whether thecondenser fans are operating at the minimum speed. If the condenser fansare operating at the minimum speed, controller 50 may turn off (block128) the condenser fans. In these embodiments, the temperature of theambient air may be low enough to cool the cooling fluid to the coolingsystem temperature set point without using electricity to operate thefans. In this mode of operation, thermosyphon cooler 12 may be operatedwithout consuming electricity. On the other hand, if controller 50determines (block 126) that the fans are not operating at the minimumfan speed, controller 50 may decrease (block 130) the fan speed.Reducing the fan speed may reduce the amount of electricity consumed bythermosyphon cooler 12.

If controller 50 determines (block 124) that the intermediatetemperature is above the cooling system temperature set point,thermosyphon cooler 12 may not be currently providing enough cooling toachieve the cooling system temperature set point. Accordingly,controller 50 may determine whether it should increase the coolingcapacity of thermosyphon cooler 12 by adjusting the speed of thecondenser fans. First, controller 50 may determine (block 132) whetherthe condenser fans are operational. If the fans are operational,controller 50 may then determine (block 134) whether the fans areoperating in an economically efficient manner. According to certainembodiments, controller 134 may calculate the current thermosyphoneconomic power consumption (TEPC) used by thermosyphon cooler 12. Forexample, controller 50 may calculate the current kilowatts being used bymotor 28 and may divide these kilowatts by the temperature differencebetween the temperature of the cooling fluid exiting process heatexchanger 18, as measured by temperature sensor 72 and temperature ofthe cooling fluid exiting thermosyphon cooler 12, as measured bytemperature sensor 70.

The controller 50 may then compare the actual TEPC to the TEPCL. If theactual TEPC is above the TEPCL, controller 50 may then decrease (block135) the fan speed. Decreasing the fan speed may reduce the amount ofcooling provided by thermosyphon cooler 12 and accordingly, more coolingmay be provided by cooling tower 14. In these instances, controller 50may increase the speed of cooling tower fan 38 to provide additionalcooling capacity. On the other hand, if the TEPC is below the TEPCL,controller 50 may increase (block 136) the speed of the condenser fansto increase the amount of cooling provided by thermosyphon cooler 12.Further, if controller 50 determines (block 132) that the fans are noton, controller 50 may turn on (block 137) the fans to the minimum fanspeed. Controller 50 may then again determine (block 124) whether theintermediate temperature is below the cooling system temperature setpoint and may then adjust operation of the condenser fans as describedabove with respect to blocks 126 to 137.

As may be appreciated, a certain amount of hysteresis may be employedwhen varying operation of the condenser fans. For example, in certainembodiments, controller 50 may adjust operation of the condenser fansafter detecting a threshold amount of change in the intermediatetemperature, as measured by temperature sensor 70.

FIG. 8 depicts various input and outputs that may be used by controller50 to govern operation of cooling system 10. As described above, theinput and outputs may be analog and/or digital outputs and may be usedby controller 50 to enable the freeze protection system 56 and to governoperation of thermosyphon cooler 12 and cooling tower 14. Further, incertain embodiments, the inputs and outputs shown in FIG. 7 may beemployed by controller 50 to determine when to direct the cooling fluidthrough thermosyphon cooler 12, through cooling tower 14, or throughboth thermosyphon cooler 12 and cooling tower 14.

Although FIGS. 6 and 7 describe method 100 in the context of athermosyphon cooler, in other embodiments, portions of method 100 may beemployed to control cooling systems with other types of dry heatrejection systems, such as dry coolers used in conjunction with a freezeprotectant coolant. FIG. 9 depicts another embodiment of cooling system10, which includes a dry cooler 142 and a heat exchanger 144. Accordingto certain embodiments, dry cooler 142 may be similar to the air cooledcondenser 78 employed within thermosyphon cooler 12. However, in otherembodiments, any suitable air cooled condenser or other type of dry heatrejection device may be used. As used herein, the term “dry heatrejection device” may refer to a heat transfer device that does notemploy wet or evaporative cooling. According to certain embodiments,heat exchanger 144 may be similar to the evaporator 76 employed in thethermosyphon cooler 12. However, in other embodiments, any suitable typeof heat exchanger, such as a plate heat exchanger, may be employed.

As shown in FIG. 9, cooling system 10 includes a dry heat rejectionsystem that includes heat exchanger 144, dry cooler 142, a freezeprotectant coolant loop 138, such as a glycol or brine loop, and a pump140. The cooling fluid from process heat exchanger 18 may flow throughheat exchanger 144, where the cooling fluid may transfer heat to thefreeze protectant coolant, such as glycol or brine, flowing through heatexchanger 144. The cooling fluid may then exit heat exchanger 144 andflow to cooling tower 14 where the cooling fluid may be further cooledas described above with respect to FIG. 1. In certain embodiments whereheat exchanger 144 is a shell and tube heat exchanger, the cooling fluidmay flow through the tubes of heat exchanger 144 while freeze protectantcoolant, such as a glycol or brine, flows through the shell side of heatexchanger 144.

Within the dry heat rejection system, the heated freeze protectantcoolant from heat exchanger 144 may flow through coolant loop 138 to drycooler 142 via pump 140. Although not shown, pump 140 may be driven byone or more motors. Within dry cooler 142, the freeze protectant coolantmay be cooled by air that is directed through dry cooler 142 by fans 26.The cooled coolant may then exit dry cooler 142 and return to heatexchanger 144 where the coolant may again absorb heat from the coolingfluid flowing through heat exchanger 144.

Because of the additional freeze protectant coolant loop 138, thecooling fluid may be contained within building 16 and may not be exposedto the ambient air. Accordingly, a freeze protection system may not beemployed because the cooling system may be protected from low ambienttemperatures by building 16. Accordingly, blocks 102 to 112 of method100 (FIG. 6) may be omitted when operating the embodiment of the coolingsystem shown in FIG. 9. However, as shown in FIG. 10, a method 146 thatis similar to blocks 114 to 137 of FIG. 7 may be employed to operate thedry heat rejection system shown in FIG. 9.

As shown in FIG. 10, method 146 may begin by detecting (block 148) thatcooling system 10 is operating in a process cooling mode. For example,controller 50 may detect operation in the process cooling mode based onthe positions of valves 24 and 32. If controller 50 detects that thesystem is operating in a process cooling mode, controller 50 may thencalculate (block 150) the dry heat rejection economic power consumptionlimit (DEPCL).

The DEPCL may be similar to the TEPCL described above with respect toFIGS. 5 to 7. For example, the DEPCL may be the maximum kilowatts ofelectricity used by the dry heat rejection system per degree of coolingfluid temperature drop achieved by the dry heat rejection system toensure that the avoided water costs are greater than the incrementalelectricity costs used to operate the dry heat rejection system. Forexample, as shown in FIG. 8, the electricity costs may be based on theelectrical consumption of motor 28 used to drive fans 26, as well as theelectricity used by the motor that drives pump 140. Controller 50 maythen calculate (block 152) the dry heat rejection system start threshold(DST). The DST may be similar to the TST described above with respect toFIGS. 5 to 7. For example, the DST may be the minimum temperaturedifference that should exist between the temperature of the coolingfluid exiting the process heat exchanger, as measured by sensor 72, andthe ambient temperature, as measured by temperature sensor 68, that isknown to enable an actual power consumption of the dry heat rejectionsystem, which is below the DEPCL.

Controller 50 may then use the calculated DST to determine (block 154)whether the actual temperature difference between the cooling fluidexiting process heat exchanger 18 and the ambient air is greater thanthe DST. If the actual temperature difference is below the DST,controller 50 may disable (block 156) operation of the dry heatrejection system. For example, controller 50 may position valve 24 todirect the cooling fluid to bypass heat exchanger 144 and flow directlythrough valve 32 to cooling tower 14. Further, in certain embodiments,controller 50 may turn off fans 26 and pump 140.

On the other hand, if controller 50 determines (block 154) that theactual temperature difference is greater than the DST, controller 50 mayenable (block 158) the dry heat rejection system. For example,controller 50 may adjust valve 24 to direct the cooling fluid throughheat exchanger 144 to transfer heat from the cooling fluid to the freezeprotectant coolant that flows through dry cooler 142. Further,controller 50 may turn on fans 26 and pump 140. Moreover, while the dryheat rejection system is operating, controller 50 may govern operationof fans 26 as described above in FIG. 6 with respect to blocks 124 to137.

FIG. 11 depicts another embodiment of cooling system 10 that includesthermosyphon cooler 12 and an open loop cooling tower 160, which is anatural draft hyperbolic cooling tower. A steam condenser 162 may beused to transfer heat from steam from a turbine to cooling system loop22. According to certain embodiments, the cooling system 10 may be usedto provide cooling for a power plant. The cooling system shown in FIG.11 may operate generally similar to the cooling system described abovewith respect to FIG. 1, and method 100 may be employed to operate thecooling system, as described above with respect to FIGS. 6 and 7.

FIG. 12 depicts another embodiment of a method 164 that may be employedto govern operation of a cooling system 10 that includes an open loopcooling tower, as shown in FIGS. 1, 4, and 11 or a closed loop coolingtower, as shown in FIG. 5. Method 164 may be generally similar to thefreeze protection portion of method 100 that is shown in FIG. 6.However, rather than employing a single evaporator temperature set pointto determine when to initiate a freeze protection sequence, method 164employs a high evaporator temperature set point and a low evaporatortemperature set point.

Method 164 may begin by determining (block 166) whether cooling system10 is beginning operation. For example, cooling system 10 may beginoperation upon startup of process heat exchanger 18. If cooling system10 is beginning operation, controller 50 may initiate (block 168) thefreeze protection mode of freeze protection system 56. The freezeprotection mode may be initiated in a manner similar to that describedabove with respect to block 103 of FIG. 6. For example, to initiate thefreeze protection mode, controller 50 may position valve 24 to directthe cooling fluid to bypass thermosyphon cooler 12. Controller 50 alsomay leave valves 60, 62, and 66 in the open position. Further,controller 50 may close valve 93 to stop the flow of refrigerant withinrefrigerant loop 80 of thermosyphon cooler 12.

If cooling system 10 is not beginning operation, controller 50 maydetermine (block 170) whether to initiate the freeze protection mode.For example, controller 50 may receive the ambient temperature as aninput from temperature sensor 68 and may determine whether the ambienttemperature is below an ambient temperature set point, which, in certainembodiments, may be 36° F. However, in other embodiments, the ambienttemperature set point may vary. If the ambient temperature is below theambient temperature set point, controller 50 may then determine (block170) whether the evaporator temperature is below an evaporator lowtemperature set point. For example, controller 50 may receive theevaporator temperature as an input from temperature sensor 57, which mayindicate the temperature of the refrigerant within the shell side ofevaporator 76. According to certain embodiments, the evaporator lowtemperature set point may be 34° F. However, in other embodiments, theevaporator low temperature set point may vary.

If controller 50 determines that the evaporator temperature is below theevaporator low temperature set point, controller 50 may initiate (block172) the freeze protection mode. The freeze protection mode may beinitiated in a manner similar to that described above with respect toblock 108 of FIG. 6. To initiate the freeze protection mode, controller50 may adjust operation of cooling system 10 so that the cooling fluidbypasses thermosyphon cooler 12. In particular, controller 50 may turnoff the thermosyphon cooler fans 26 and may divert water away fromthermosyphon cooler 12 using valve 24. Controller 50 also may positionvalve 32 to direct the cooling fluid exiting thermosyphon cooler 12directly to sump 42. After the cooling fluid has drained fromthermosyphon cooler 12, controller 50 may position valve 32 to allow thecooling fluid to flow through cooling tower 14, where the cooling fluidmay be cooled by evaporative cooling.

In the freeze protection mode, controller 50 also may drain coolingfluid from thermosyphon cooler 12. For example, controller 50 may closevalve 30 and open valves 60 and 62 to direct the cooling fluid withinthermosyphon cooler 12 to drain line 64. Controller 50 also may openvalve 66 to inject air into thermosyphon cooler 12 to further promotedrainage of the cooling fluid from thermosyphon cooler 12. According tocertain embodiments, draining the cooling fluid from thermosyphon cooler12 in freeze protection mode may protect tubes 85 from damage due toexpansion and/or freezing of the cooling fluid. Further, controller 50may turn off supplemental heat to evaporator 76.

If the evaporator temperature is not below the evaporator lowtemperature set point, controller 50 may then determine whether theevaporator temperature is below an evaporator high temperature setpoint. For example, controller 50 may determine whether the evaporatortemperature received as an input from temperature sensor 57 is less thanthe evaporator high temperature set point. According to certainembodiments, the evaporator high temperature set point may be 42° F.However, in other embodiments, the evaporator high temperature set pointmay vary.

If controller 50 determines that the evaporator temperature is below theevaporator high temperature set point and that the ambient temperatureis below the ambient temperature set point, controller 50 may thendetermine (block 176) if there is flow through thermosyphon cooler 12.For example, controller 50 may detect flow through thermosyphon cooler12 using differential pressure switch 58.

If controller 50 determines that there is no flow through thermosyphoncooler 12, controller 50 may initiate (block 178) the low temperatureprotection mode of freeze protection system 56. The low temperatureprotection mode may be similar to that described above with respect toblock 105 of FIG. 6. For example, the low temperature protection modemay allow the cooling fluid to be retained within thermosyphon cooler 12during relatively short periods of low ambient temperatures and/orduring relatively short periods of shutdown of cooling system 10.

To initiate the low temperature protection mode, controller 50 mayadjust operation of cooling system 10 to protect the cooling fluidwithin thermosyphon cooler 12 from freezing. For example, controller 50may turn off the thermosyphon cooler fans 26. Controller 50 also mayensure that valves 24 and 30 are open to allow the cooling fluid to flowthrough thermosyphon cooler 12. Further, controller 50 may close valve93 to stop the flow of refrigerant through refrigerant loop 80. Closingvalve 93 may allow the refrigerant to collect within condenser 78, whichmay inhibit freezing of the cooling fluid within evaporator 76.Controller 50 also may turn on the supplemental heat for evaporator 76,which may provide heat to evaporator 76 to inhibit freezing of thecooling fluid contained within evaporator 76.

If, on the other hand, controller 50 determines that there is flowthrough thermosyphon cooler 12, controller 50 may initiate (block 180)the thermosyphon protection mode of freeze protection system 56. Thethermosyphon protection mode may be initiated in a manner similar to thelow temperature protection mode described above with respect to block178. However, rather than turning on the supplemental heat forevaporator 76, the supplemental heat may be turned off (or may remainoff) since there is flow through evaporator 76. According to certainembodiments, the flow of the cooling fluid through evaporator mayinhibit freezing of the cooling fluid in the evaporator, andaccordingly, the supplemental heat may not be desired. In addition toturning off the supplemental heat, controller 50 may turn off thethermosyphon cooler fans 26. Controller 50 also may ensure that valves24 and 30 are open to allow the cooling fluid to flow throughthermosyphon cooler 12. Further, controller 50 may close valve 93 tostop the flow of refrigerant through refrigerant loop 80 and allow therefrigerant to collect within condenser 78.

If controller 50 determines that none of the protection modes should beinitiated, controller 50 may then determine (block 182) whether thefreeze protection mode should be disabled. First, controller 50 maydetermine whether freeze protection mode is currently enabled, forexample, based on the positions of valves 24, 60, 62, 66, and 30. If thefreeze protection mode is currently enabled, controller 50 may thendetermine whether the intermediate temperature (i.e. the temperature ofthe cooling fluid exiting thermosyphon cooler 12), as measured bytemperature sensor 70, is above an intermediate temperature set point,which, in certain embodiments, may be approximately 50° F. However, inother embodiments, the intermediate temperature set point may vary.

If the intermediate temperature is not above the intermediatetemperature set point and/or the freeze protection mode is not currentlyenabled, controller 50 may allow cooling system 10 to continue operating(block 186) in its current mode. However, if the intermediatetemperature is above the intermediate temperature set point, controller50 may initiate (block 184) a freeze restart sequence to allow thecooling fluid to flow through thermosyphon cooler 12. The freeze restartsequence may be initiated in a manner similar to that described abovewith respect to block 112 of FIG. 6. For example, controller 50 mayclose drain valves 60 and 62 and also may close vent valve 66. Further,controller 50 may adjust the positions of valves 24 and 30 to allow thecooling fluid to flow through thermosyphon cooler 12. Accordingly,cooling system 10 may now be operating in a process cooling mode wherethe cooling fluid flows through thermosyphon cooler 12 to be cooled bythe ambient air. Controller 50 may then continue to operate (block 186)cooling system 10 in its current mode. For example, in certainembodiments, the controller 50 may then govern operation of coolingsystem 10 as described above with respect to blocks 114 to 137 of FIG.7.

FIG. 13 depicts another embodiment of cooling system 10 that includesopen loop cooling tower 14 and thermosyphon cooler 12. The embodiment ofcooling system 10 shown in FIG. 13 is generally similar to theembodiment of cooling system 10 described above with respect to FIG. 4.However, rather than including a freeze protection system 56 thatenables draining of the cooling fluid from evaporator 76, the coolingsystem 10 shown in FIG. 13 includes a freeze protection system 188 thatprovides supplemental heating when freeze protection is desired.

The freeze protection system 188 includes one or more heaters 190 thatare powered by a power supply 192. Heaters 190 may include heat tracing,cartridge heaters, or a combination thereof, as well as other types ofelectric heaters. According to certain embodiments, heaters 190 mayinclude cartridge heaters that extend into shell 84 (FIG. 3) ofevaporator 76 to heat the refrigerant circulating within the shell.Further, in certain embodiments, the exterior of evaporator shell 84 maybe insulated to enhance heat retention within evaporator 76. Powersupply 192 may include one or more batteries or other type of powersupply, such as a generator or system standby power system, amongothers. In certain embodiments, power supply 192 may be an independentpower source, such as one or more batteries, that solely powers heaters190. However, in other embodiments, power supply 192 may be a backup orstandby power system designed to provide power for other equipmentand/or processes in a facility employing cooling system 10. Further,although freeze protection system 188 is shown in FIG. 13 as part of acooling system 10 that includes an open loop cooling tower with anintegrated sump, in other embodiments, freeze protection system 188 maybe employed in other types of cooling systems 10, such as those shown inFIGS. 1, 5, and 11.

Controller 50 may govern operation of freeze protection system 188.According to certain embodiments, controller 50 may be communicativelycoupled to power supply 192 to turn on heaters 190 when freezeprotection is desired. For example, controller 50 may send a controlsignal to power supply 192 to enable heaters 190 when the ambienttemperature, as detected by sensor 68, is below an ambient temperatureset point. In another example, controller 50 may enable heaters 190 whenthe evaporator temperature, as detected by sensor 57 is below anevaporator temperature set point. In a further example, controller 50may disable heaters 190 when the temperature of the cooling fluidexiting thermosyphon cooler 12, as detected by sensor 70, is above anintermediate temperature set point.

According to certain embodiments, the cooling systems 10 describedherein may be designed and installed as new cooling systems. However, asdescribed below with respect to FIGS. 14 to 16, in other embodiments,existing cooling systems may be retrofit to produce the cooling systemsdescribed herein.

FIG. 14 depicts a prior art cooling system 194 that may be retrofit toinclude the cooling systems described herein. Cooling system 194includes a cooling system loop 196 that circulates a cooling fluidbetween process heat exchanger 18 and cooling tower 14. As the coolingfluid flows through process heat exchanger 18, the cooling fluid absorbsheat from the process fluid flowing through process loop 20. The coolingfluid then flows through valve 32 to cooling tower 14 where the coolingfluid may be cooled via evaporative cooling with ambient air. Withincooling tower 14, nozzles 34 direct the cooling fluid over fill material36, and a fan 38 directs air up through the cooling tower. The cooledcooling fluid may then exit cooling tower 14 and may be collected withinsump 42. Valve 44 may be opened to direct makeup cooling fluid into sump42, and valve 46 may be opened to remove a portion of the cooling fluid,which may contain minerals, salts, and other contaminants, as blowdown.As shown, sump 42 is an integral part of cooling tower 14; however, inother embodiments, sump 42 may be located within building 16, as shownin FIG. 1. Further, although the cooling tower is shown as an open loopcooling tower 14, in other embodiments, cooling tower 14 may be a closedloop cooling tower 94, as shown in FIG. 5, or a hyperbolic cooling tower160, as shown in FIG. 11.

The cooling system 14 also includes temperature sensor 72, which detectsthe temperature of the cooling fluid exiting process heat exchanger 18,and temperature sensor 74, which detects the temperature of the coolingfluid entering process heat exchanger 18. In certain embodiments,temperature sensors 72 and 74 may provide the temperatures to acontroller (not shown) in the form of input signals, which may be usedto control operation of cooling system 194.

As shown in FIG. 15, cooling system 194 may be retrofit with athermosyphon cooling system 198 to form an embodiment of cooling system10 that includes thermosyphon cooler 12. For example, piping 200 may becoupled to cooling system loop 196 at connection points 202 and 204 tofluidly couple cooling system loop 196 to thermosyphon cooler 12. Valve24 may be inserted at connection point 202, and a piping connection 204,such as a T-connection, may be inserted at connection 206 point 204 tocouple cooling system loop 196 to piping 200. Piping 200 may form athermosyphon cooling system loop that circulates the cooling fluid fromexisting cooling system loop 196 to thermosyphon cooler 12.

Thermosyphon cooler 12 and its associated equipment may be coupled topiping 200 to circulate the cooling fluid through thermosyphon cooler12. Further, controller 50 may be installed to govern operation ofcooling system 10. In certain embodiments, controller 50 may beintegrated with, or may replace, an existing controller for coolingsystem 194. Existing sensors 72 and 74 may be communicatively coupled tocontroller 50. Further, in certain embodiments, flow meter 47 may beinstalled to measure the flow rate of the make up water entering sump 42through valve 44.

FIG. 16 depicts another embodiment of a thermosyphon cooling system 208that may be added to existing cooling system 194 to form an embodimentof cooling system 10. In this embodiment, piping 210 may be coupled tocooling system loop 196 at connection points 202 and 204 to fluidlycouple cooling system loop 196 to thermosyphon cooler 12. Valve 24 maybe inserted at connection point 202, and piping connection 206 may beinserted at connection point 204 to couple cooling system loop 196 topiping 210. Further, valves 60, 62, and 30, and differential pressureswitches 58 may be installed in piping 210 to form freeze protectionsystem 56. Drain line 64 also may be connected to piping 210 to providefor drainage of cooling fluid from piping 210 and evaporator 76.

Thermosyphon cooler 12 and its associated equipment may be coupled topiping 210 to circulate the cooling fluid through thermosyphon cooler12, and controller 50 may be installed to govern operation of coolingsystem 10. Further, valve 66 and its corresponding vent line may beinstalled to inject air into thermosyphon cooler 12 to facilitatedrainage of the cooling fluid from thermosyphon cooler 12. Existingsensors 72 and 74 may be communicatively coupled to controller 50.Further, in certain embodiments, flow meter 47 may be installed tomeasure the flow rate of the make up water entering sump 42 throughvalve 44.

While only certain features and embodiments of the invention have beenillustrated and described, many modifications and changes may occur tothose skilled in the art (e.g., variations in sizes, dimensions,structures, shapes, and proportions of the various elements, values ofparameters (e.g., temperatures, pressures, etc.), mounting arrangements,use of materials, orientations, etc.) without materially departing fromthe novel teachings and advantages of the subject matter recited in theclaims. For example, the order or sequence of any process or methodsteps may be varied or re-sequenced according to alternativeembodiments. Further, although individual embodiments are discussedherein, the disclosure is intended to cover all combinations of theseembodiments. It is, therefore, to be understood that the appended claimsare intended to cover all such modifications and changes as fall withinthe true spirit of the invention. Furthermore, in an effort to provide aconcise description of the exemplary embodiments, all features of anactual implementation may not have been described (i.e., those unrelatedto the presently contemplated best mode of carrying out the invention,or those unrelated to enabling the claimed invention). It should beappreciated that in the development of any such actual implementation,as in any engineering or design project, numerous implementationspecific decisions may be made. Such a development effort might becomplex and time consuming, but would nevertheless be a routineundertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure, without undueexperimentation.

1. A method for operating a cooling system, comprising: determining atemperature of a cooling fluid exiting a dry heat rejection device;comparing the temperature of the cooling fluid exiting the dry heatrejection device to a cooling temperature set point; reducing a fanspeed of one or more fans of the dry heat rejection device when thetemperature of the cooling fluid exiting the dry heat rejection deviceis less than the cooling temperature set point; determining an economicefficiency of operation of the one or more fans of the dry heatrejection device based on a water cost, or an electricity cost, or bothwhen the temperature of the cooling fluid exiting the dry heat rejectiondevice equals or exceeds the cooling temperature set point; increasingthe fan speed of the one or more fans of the dry heat rejection devicewhen the economic efficiency of operation of the one or more fans of thedry heat rejection device exceeds a threshold and when the temperatureof the cooling fluid exiting the dry heat rejection device equals orexceeds the cooling temperature set point; and reducing the fan speed ofthe one or more fans of the dry heat rejection device and initiatingoperation of a cooling tower when the economic efficiency of operationof the one or more fans of the dry heat rejection device is less than orequal to the threshold and when the temperature of the cooling fluidexiting the dry heat rejection device equals or exceeds the coolingtemperature set point.
 2. The method of claim 1, comprising maintainingthe fan speed of the one or more fans of the dry heat rejection devicewhen the temperature of the cooling fluid exiting the dry heat rejectiondevice is generally equal to the cooling temperature set point and whenthe economic efficiency of operation of the one or more fans of the dryheat rejection device equals or exceeds the threshold.
 3. The method ofclaim 1, wherein reducing the fan speed of the one or more fans of thedry heat rejection device when the temperature of the cooling fluidexiting the dry heat rejection device is less than the coolingtemperature set point comprises turning off the one or more fans of thedry heat rejection device when the fan speed of the one or more fans ofthe dry heat rejection device is at a base speed.
 4. The method of claim1, wherein reducing the fan speed of the one or more fans of the dryheat rejection device when the economic efficiency of operation of theone or more fans of the dry heat rejection device is less than or equalto the threshold and when the temperature of the cooling fluid exitingthe dry heat rejection device equals or exceeds the cooling temperatureset point comprises reducing the fan speed of the one or more fans to abase fan speed.
 5. The method of claim 1, wherein determining theeconomic efficiency of operation of the one or more fans of the dry heatrejection device based on a water cost, or an electricity cost, or bothcomprises calculating an economic power consumption of the dry heatrejection device.
 6. The method of claim 5, wherein calculating theeconomic power consumption of the dry heat rejection device comprisesdividing current kilowatts consumed by a motor of the one or more fansby a temperature differential between the temperature of the coolingfluid exiting the dry heat rejection device and an additionaltemperature of the cooling fluid exiting a process heat exchanger of thecooling system positioned upstream of the dry heat rejection device. 7.The method of claim 6, comprising determining a differential between aneconomic power consumption limit and the economic power consumption ofthe dry heat rejection device, wherein the economic power consumptionlimit is determined based on the water cost, or the electricity cost, orboth.
 8. The method of claim 7, comprising comparing the differentialbetween the economic power consumption of the dry heat rejection deviceand the power consumption limit to the threshold.
 9. The method of claim1, wherein initiating operation of the cooling tower comprisesincreasing an additional fan speed of one or more additional fans of thecooling tower.
 10. One or more tangible, non-transitory machine-readablemedia comprising processor-executable instructions to: receive feedbackindicative of a temperature of a cooling fluid exiting a dry heatrejection device from a temperature sensor; compare the temperature ofthe cooling fluid exiting the dry heat rejection device to a coolingtemperature set point; reduce a fan speed of one or more fans of the dryheat rejection device when the temperature of the cooling fluid exitingthe dry heat rejection device is less than the cooling temperature setpoint; determine an economic efficiency of operation of the one or morefans of the dry heat rejection device based on a water cost, or anelectricity cost, or both when the temperature of the cooling fluidexiting the dry heat rejection device equals or exceeds the coolingtemperature set point; increase the fan speed of the one or more fans ofthe dry heat rejection device when the economic efficiency of operationof the one or more fans of the dry heat rejection device exceeds athreshold and when the temperature of the cooling fluid exiting the dryheat rejection device equals or exceeds the cooling temperature setpoint; and reduce the fan speed of the one or more fans of the dry heatrejection device and initiate operation of a cooling tower when theeconomic efficiency of operation of the one or more fans of the dry heatrejection device is less than or equal to the threshold and when thetemperature of the cooling fluid exiting the dry heat rejection deviceequals exceeds the cooling temperature set point.
 11. The one or moretangible, non-transitory machine-readable media of claim 10, wherein theprocessor-executable instructions are configured to monitor a change inthe temperature of the cooling fluid exiting the dry heat rejectiondevice over a set time.
 12. The one or more tangible, non-transitorymachine-readable media of claim 11, wherein the processor-executableinstructions are configured to adjust the fan speed of the one or morefans of the dry heat rejection device when the change in the temperatureof the cooling fluid exiting the dry heat rejection device exceeds anadditional threshold over the set time.
 13. The one or more tangible,non-transitory machine-readable media of claim 10, wherein theprocessor-executable instructions are configured to re-compare thetemperature of the cooling fluid exiting the dry heat rejection deviceto the cooling temperature set point after adjusting the fan speed ofthe one or more fans of the dry heat rejection device.
 14. The one ormore tangible, non-transitory machine-readable media of claim 10,wherein the processor-executable instructions are configured to increasean additional fan speed of one or more additional fans of the coolingtower to initiate operation of the cooling tower when the economicefficiency of operation of the one or more fans of the dry heatrejection device is less than or equal to the threshold and when thetemperature of the cooling fluid exiting the dry heat rejection deviceequals or exceeds the cooling temperature set point.
 15. A coolingsystem, comprising: a cooling fluid loop configured to circulate acooling fluid therethrough; a dry heat rejection device disposed alongthe cooling fluid loop and configured to transfer heat from the coolingfluid to ambient atmosphere through dry cooling; a cooling towerdisposed downstream of the dry heat rejection device along the coolingfluid loop and configured to transfer heat from the cooling fluid to theambient atmosphere through evaporative cooling; and a controllerconfigured to: receive feedback indicative of a temperature of thecooling fluid exiting the dry heat rejection device from a temperaturesensor; compare the temperature of the cooling fluid exiting the dryheat rejection device to a cooling temperature set point; reduce a fanspeed of one or more fans of the dry heat rejection device when thetemperature of the cooling fluid exiting the dry heat rejection deviceis less than the cooling temperature set point; determine an economicefficiency of operation of the one or more fans of the dry heatrejection device based on a water cost, or an electricity cost, or bothwhen the temperature of the cooling fluid exiting the dry heat rejectiondevice equals or exceeds the cooling temperature set point; increase thefan speed of the one or more fans of the dry heat rejection device whenthe economic efficiency of operation of the one or more fans of the dryheat rejection device exceeds a threshold and when the temperature ofthe cooling fluid exiting the dry heat rejection device equals orexceeds the cooling temperature set point; and reduce the fan speed ofthe one or more fans of the dry heat rejection device and initiateoperation of the cooling tower when the economic efficiency of operationof the one or more fans of the dry heat rejection device is less thanthe threshold and when the temperature of the cooling fluid exiting thedry heat rejection device equals or exceeds the cooling temperature setpoint.
 16. The system of claim 15, wherein the controller is configuredto maintain the fan speed of the one or more fans of the dry heatrejection device when the temperature of the cooling fluid exiting thedry heat rejection device is generally equal to the cooling temperatureset point and when the economic efficiency of operation of the one ormore fans of the dry heat rejection device equals or exceeds thethreshold.
 17. The system of claim 15, wherein the controller isconfigured to turn off the one or more fans of the dry heat rejectiondevice when the fan speed of the one or more fans of the dry heatrejection device is at a base speed, when the temperature of the coolingfluid exiting the dry heat rejection device is less than the coolingtemperature set point.
 18. The system of claim 15, wherein thecontroller is configured to turn off the one or more fans of the dryheat rejection device when the economic efficiency of operation of theone or more fans of the dry heat rejection device is less than thethreshold.
 19. The system of claim 15, wherein the controller isconfigured to receive inputs indicative of the water cost, or theelectricity cost, or both from an operator.
 20. The system of claim 15,wherein the controller is configured to receive inputs indicative of thewater cost, or the electricity cost, or both from a computer network.